High-Performance A-Site Deficient Perovskite Electrocatalyst for Rechargeable Zn–Air Battery

Round 1

Reviewer 1 Report

In this revised version there are some aspects that need to be considered. There is no discussion on the correlation between electrochemical activity and electrochemical performance. In "Tafel" figure overpotential and not potential must be used. To see if a material is good or not not only, it is necessary to consider not only  Tafel plot but also exchange current.

Author Response

Thanks for your question. We have already corrected the Tafel figure for overpotential instead of potential. We agreed with what you mentioned that Tafel plot was not only a parameter for evaluating the electrochemical activity. From our tested result, it can be seen that the maximum current density measured at 2.0 V was 27 mA cm⁻² for (SmSr)_0.95Co_0.9Pt_0.1O₃, which was similar to that of BSCF (26.7 mA cm⁻²). So the maximum current density was still promising for this pervoskite.

Reviewer 2 Report

The manuscript entitled “High-Performance A-site deficient Perovskite Electrocatalyst for Zn-Air Battery” by Chengcheng Wang et al describes the synthesis of perovskite (SmSr)0.95Co0.9Pt0.1O3) electrocatalyst for OER. Moreover, the authors claim that the synthesized material can be used for Zn-air battery. The manuscript can be published in the journal after the major revision to clarify the following comments.

1) Authors claim in the introduction part that “Hence, it is urgent to develop non-platinum substances to replace RuO₂ and IrO₂ electrocatalysts”. Then, it is not clear from the manuscript why did they use Pt where Pt is not a good OER active catalyst. The authors should justify the inclusion of Pt in the Perovskite?

2) According to the author, “The sample showed rhombohedral perovskite, which was similar to that of published results [31]”. How could authors conclude that the synthesized material is rhombhohedral? Secondly, what does it mean similar to the published results, whereas ref 31 dealt with different material? What is the inverted triangle inside the XRD? Authors should explain the XRD in detail.

3) Authors claim that “Nanoparticles were similar to be columnar and the average size of around 150-250 nm”- From the SEM image in Figure 2, how did they find the particle size from the agglomerated structure. Authors should take a clear picture of SEM in order to claim the particle size is in the range of 150-250 nm.

4) Authors didn’t explain Figure 2c and Figure 2d in the main text. Authors are advised to explain the figures for the materials.

5) Before taking the elemental mapping of the materials, authors should take EDS for the materials and show the atomic % of each element.

6) According to the cited paper (ref 37), 530.5 eV is assigned to oxygen in the form of O₂^2-/O^- on the surface, however, in the present manuscript, there is no peak at 530.4 eV (page 4, line 123). Then, how did the authors claim that the peak is due to the O₂^2-/O^-?

 

7) Authors should clearly mention how they did they calculate the onset potential. From Figure 5a, it is clear that the onset potential is above 1.55 V, the how authors could claim that it is 1.50 V where a flat line-no current increase is observed. Moreover, according to the previous literature (ref 29), it was shown that the onset potential for BSCF was found to be 1.61 V under similar conditions, however, the present manuscript showed 1.55 V. How could the authors explain this discrimination in values?

8) Authors explain that A-site deficient perovskite is good for Zn-air battery based on OER data, didn’t show any ORR data before claiming it air-battery. Without showing any ORR data, how were the charging and discharging current density (5 mAcm-2) and time (10 min) fixed? Authors are advised to explain Zn-air battery in detail.

Author Response

The manuscript entitled “High-Performance A-site deficient Perovskite Electrocatalyst for Zn-Air Battery” by Chengcheng Wang et al describes the synthesis of perovskite (SmSr)_0.95Co_0.9Pt_0.1O₃) electrocatalyst for OER. Moreover, the authors claim that the synthesized material can be used for Zn-air battery. The manuscript can be published in the journal after the major revision to clarify the following comments.

 

• Authors claim in the introduction part that “Hence, it is urgent to develop non-platinum substances to replace RuO2 and IrO2 electrocatalysts”. Then, it is not clear from the manuscript why did they use Pt where Pt is not a good OER active catalyst. The authors should justify the inclusion of Pt in the Perovskite?

Answer: Thanks for your question. From our point of view, this paper was mainly focused on studying A-site deficient perovskite electrocatalysts. Moreover, Pt element was only incorporated into the B-site of pervoskites, which was different from the Pt was used as OER catalyst. The purpose of Pt element in B site pervoskite was only added to improve the electrical conductivity of this pervoskite oxide.

 

• According to the author, “The sample showed rhombohedral perovskite, which was similar to that of published results [31]”. How could authors conclude that the synthesized material is rhombhohedral? Secondly, what does it mean similar to the published results, whereas ref 31 dealt with different material? What is the inverted triangle inside the XRD? Authors should explain the XRD in detail.

Answer: Sorry for our wrong description. We have already corrected the description in the discussion part. The tested result of XRD can only indicate that the powders were perovskite structure, which was similar the reference paper regarding or SmSrCoO₃. We need to calculate the a, b, and c of the crystal to identify whether it is rhombohedral or cubic structure. The inverted triangles in the XRD pattern indicated that were referred to different crystal planes of perovskite structure.

• Authors claim that “Nanoparticles were similar to be columnar and the average size of around 150-250 nm”- From the SEM image in Figure 2, how did they find the particle size from the agglomerated structure. Authors should take a clear picture of SEM in order to claim the particle size is in the range of 150-250 nm.

Answer: We have already shown the SEM image below. We selected the representative testing data in the SEM picture. The size ranges from 150-250 nm. P1=183.3 nm, P2=230.2 nm, P3=231.4 nm, P4=223.1 nm, P5=169.9 nm, P6=145.6 nm, P7=161.6 nm.

 

• Authors didn’t explain Figure 2c and Figure 2d in the main text. Authors are advised to explain the figures for the materials.

Answer:We have already added more explanation in the manuscript and highlighted them in yellow.

 

• Before taking the elemental mapping of the materials, authors should take EDS for the materials and show the atomic % of each element.

Answer: Thanks for your suggestions. We agreed that we need to do the EDS test for the materials. We did element mapping of the pervoskite, moreover, we even have already done ICP test to get the atmoic ratio of this pervoskite.

 

• According to the cited paper (ref 37), 530.5 eV is assigned to oxygen in the form of O2 2- /O on the surface, however, in the present manuscript, there is no peak at 530.4 eV (page 4, line 123). Then, how did the authors claim that the peak is due to the O2 2- /O- ?

Answer: According to what we mentioned, the binding energy that we got from the curve was related to the deconvoluted results. The first one was 530.4 eV and and the second one was 531.4 eV. And then we searched for some papers in Ref 37 and we got the conclusion that good OER activity in an alkaline solution might be attributed to O₂^2-/O^- on the surface of catalysts.

 

• Authors should clearly mention how they did they calculate the onset potential. From Figure 5a, it is clear that the onset potential is above 1.55 V, the how authors could claim that it is 1.50 V where a flat line-no current increase is observed. Moreover, according to the previous literature (ref 29), it was shown that the onset potential for BSCF was found to be 1.61 V under similar conditions, however, the present manuscript showed 1.55 V. How could the authors explain this discrimination in values?

Answer: Sorry for our wrong data. We identified the definition of onset potential of ORR, in which can indicate that when the current starts to increase, it refers to the onset potential.

• Authors explain that A-site deficient perovskite is good for Zn-air battery based on OER data, didn’t show any ORR data before claiming it air-battery. Without showing any ORR 2 data, how were the charging and discharging current density (5 mAcm-2) and time (10 min) fixed? Authors are advised to explain Zn-air battery in detail.

Answer: Thanks for your suggestion. In this manuscript, we were mainly focused on studying the OER activity of pervoskites. Then we tried to assemble the Zinc-air battery, and then we tested the charging and discharging activity of the cell. We used the testing parameter according to the reference we listed below.

[1] Xixi Wang, Jaka Sunarso, Qian Lu, Ziling Zhou, Jie Dai, Daqin Guan, Wei Zhou,* and Zongping Shao*High-Performance Platinum-Perovskite Composite Bifunctional Oxygen Electrocatalyst for Rechargeable Zn–Air Battery.Adv. Energy Mater. 2020, 10, 1903271.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

        

Author Response

Dear Reviewers,

 

Thanks for your suggestion. We have already corrected the question you mentioned. Please have a look. Thanks!

1. The triangles inside the XRD should be labeled.

Answer: Thanks. We have already labeled the crystal plane in the figure.

1. Without showing any ORR activity, how did the authors confirm that the material could be used in the Zn - air battery? In the given reference, the material was used as bi-functional material- showing both OER and ORR.

Answer: In this paper, we are mainly focused on studying the OER activity of this pervoskite. Compared with ORR activity, OER activity of this perovskite was more obvious and excellent, which was even comparable to BSCF. So that’s why we didn’t show the ORR activity value. Moreover, the Zn-air battery in this manuscript refers to Rechargeable battery, which can involve ORR and OER of the air electrode side. So we have all changed the name from Zn-air battery to Rechargeable Zn-air battery.

• Author mentioned that they have discussed Fig. 2c and 2d, however, the discussion is incomplete in the revised manuscript.

Answer: Thanks. We have already added more discussions in the manuscript.

1. iv) How did the authors know that the inclusion of Pt will increase the conductivity? Is there any reference? If yes, then this justification should be included in the main manuscript.

Answer: From our point of view, perovskite oxides were able to show good OER activities because of increasing ionic, electronic conductivities and flexible compositional diversification properties. Moreover, there are some researches regarding to A-site deficiency perovskite. So that’s why we are trying to investigate this kind of A-site pervoskites (SmSr)_0.95Co_0.9Pt_0.1O₃.

1. v) ICP test results should be included in the main manuscript.

Answer: We have already added ICP test results in the manuscript and highlighted them in yellow.

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have answered most of the comments. A few comments before it can be accepted for the Catalysts.

i) The triangles inside the XRD should be labeled.

ii) Without showing any ORR activity, how did the authors confirm that the material could be used in the Zn - air battery? In the given reference, the material was used as bi-functional material- showing both OER and ORR.

iii) Author mentioned that they have discussed Fig. 2c and 2d, however, the discussion is incomplete in the revised manuscript.

iv) How did the authors know that the inclusion of Pt will increase the conductivity? Is there any reference? If yes, then this justification should be included in the main manuscript.

v) ICP test results should be included in the main manuscript.

 

 

Author Response

Dear Reviewers,

 

Thanks for your suggestion. We have already corrected the question you mentioned. Please have a look. Thanks!

1. The triangles inside the XRD should be labeled.

Answer: Thanks. We have already labeled the crystal plane in the figure.

1. Without showing any ORR activity, how did the authors confirm that the material could be used in the Zn - air battery? In the given reference, the material was used as bi-functional material- showing both OER and ORR.

Answer: In this paper, we are mainly focused on studying the OER activity of this pervoskite. Compared with ORR activity, OER activity of this perovskite was more obvious and excellent, which was even comparable to BSCF. So that’s why we didn’t show the ORR activity value. Moreover, the Zn-air battery in this manuscript refers to Rechargeable battery, which can involve ORR and OER of the air electrode side. So we have all changed the name from Zn-air battery to Rechargeable Zn-air battery.

• Author mentioned that they have discussed Fig. 2c and 2d, however, the discussion is incomplete in the revised manuscript.

Answer: Thanks. We have already added more discussions in the manuscript.

1. iv) How did the authors know that the inclusion of Pt will increase the conductivity? Is there any reference? If yes, then this justification should be included in the main manuscript.

Answer: From our point of view, perovskite oxides were able to show good OER activities because of increasing ionic, electronic conductivities and flexible compositional diversification properties. Moreover, there are some researches regarding to A-site deficiency perovskite. So that’s why we are trying to investigate this kind of A-site pervoskites (SmSr)_0.95Co_0.9Pt_0.1O₃.

1. v) ICP test results should be included in the main manuscript.

Answer: We have already added ICP test results in the manuscript and highlighted them in yellow.

 

 

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This paper shows some data about electrocatalytic properties toward OER of some perovskite materials. The work is interesting, there are some major  remarks:

• line 24-26 (abstract) have similar meaning
• line 46 "it was easy to be amorphous after long-time test." It is difficult to understand the eaning of this statement
• Table 1. It is necessary to report the standard deviation of the reported values

Considering the discussion of Tafel slope values it is important to evidence whether the RDS of the process for this materials is an adsorption process, as it is typical for oxide materials. In this case the variation of the slope could be justified considering a variation of lateral interaction parameter between adsorbed particles. A variation of transfer coefficient could also be a valid justification of this variation.

• the baseline of XPS convolution is wrong in Fig. 4b and 4c

Author Response

• Extensive editing of English language and style required.

Answer: We have already polished the language.

• line 24-26 (abstract) have similar meaning

Answer: We have already deleted the similar sentence.

• line 46 "it was easy to be amorphous after long-time test." It is difficult to understand the meaning of this statement

Answer: We have already changed this sentence and highlighted them in yellow.

• Table 1. It is necessary to report the standard deviation of the reported values

Answer: We have already added the standard deviation of the values.

• the baseline of XPS convolution is wrong in Fig. 4b and 4c

Answer: We have already refitted the XPS spectra of Fig.4b and 4c.

Reviewer 2 Report

In their recent manuscript entitled: High-Performance A-site deficient Perovskite Electrocatalyst for Zn-Air Battery, Cheng Cheng Wang et al. report on the synthesis and the investigation of a novel catalyst material with respect to its electrocatalytic performance for the oxygen evolution reaction (OER). According to the author’s description, the synthesized material would be an A-site deficient perovskite containing, Sm, Sr, Co and Pt with the following stoichiometry: (SmSr)_0.95Co_0.9Pt_0.1O₃ (in the following abbreviated by: SSCP). For their investigation the authors applied XRD, SEM, HRTEM, HADDF, XPS, BET, LSV, CP and Zn-Air battery full cell testing. Based on their investigation, the authors claim SSCP would be a highly efficient OER electrocatalyst that exhibits high cycle stability.  

Research on the electrocatalytic properties of various perovskites for the OER is an extensively investigated branch of electrochemistry with a considerable number of papers published every year. However, despite this elevated number of papers, the manuscript provided by Cheng Cheng Wang et al. appears to be the first reporting on SSCP. Accordingly, the subject of the present manuscript is of general interest for the scientific community. Nevertheless, the reviewer cannot recommend the manuscript for publication in well-respected journal such as MDPI Catalysts (Impact Factor: 4.2), due to numerous unjustified statements, inconsistencies and an insufficient description of the results.   

These are the reviewer’s comments structured as follows: general comment, language and content.

General comment:

The reviewer recognizes the tendency to apply magniloquent terms in science in order to advertise own research. However, the reviewer does not agree that SSCP exhibits excellent electrocatalytic performance that justifies frequent repetition of this claim. This is due the following:

• SSCP is not compared to a commercial reference such as IrO₂ nanoparticles, although it is the author’s intention to replace IrO₂ by a cheap alternative. Consider additional reference measurements for comparison.
• In his previous paper (org/10.1016/j.electacta.2017.06.161), Cheng Cheng Wang reports on a variety of different perovskites made of La, Sr, Ni and Fe (La_0.5Sr_0.5Ni_xFe_1-xO_3-δ, x=0.8, 0.5, 0.4, 0.2, LSNF55xx), which they compare to BSCF as well. In the previous study, LSNF 5546 was found to perform 14% better than the custom-made reference BSCF (based on j_OER). Nevertheless, in this manuscript, BSCF is chosen as a reference again, although in-house material showed better performance for a similar synthesis procedure already. Thus, in the reviewer’s opinion, SSCP cannot be considered an excellent material, since there are other materials (even without precious platinum reported by the same first author) which show even better performance. Thus, the reviewer recommends a less magniloquent description.

Language:

The quality of the English language throughout the complete manuscript is poor. The reviewer recommends professional language editing. Please pay special attention to missing definite and indefinite articles, tenses, missing and displaced words, as well as singular and plural inconsistencies. These are just a few examples from the first two manuscript pages:

Lines 15-16: Zinc-air batteries […]. However, THEIR application is. […]

Line 16: […] by slow kinetics of THE oxygen reduction [ORR] […]

Line 18: Here, AN A-site deficient […]

Line 74: Nanoparticles WERE similar to be […]

 

 

Content:

Line 71: How would the others know the exact composition of the investigated material? The XRD pattern in Fig.1 does not provide a reference and the authors do not provide theoretic calculations of the expected XRD pattern. Moreover, the authors do not provide ICP-OES results in order to prove the validity of the proposed structure. Similarity with Sm_0.5Sr_0.5CoO₃ from reference [31] allows for other stoichiometries to result from the applied synthesis as well. Consider additional investigations.

Line 74: The authors claim an average nanoparticle size of 40-200 nm, which is a quite broad distribution. Moreover, the review is unable to determine how the authors determined the average nanoparticle size. Fig. 2a shows a large agglomerate with some distinct features. What are the actual particles? Moreover the reviewer recommends to enlarge the scale bar.

Line 77: HADDF results are poorly explained despite their considerable consumption of space. 

Line 78: BET results are not shown in Fig.3

Line 129: The authors state that O₂^2-/O^- would be a reason for improved OER activity as stated by one of the indicated references (which reference is unclear to the reviewer). “Improved OER” is a relative term. Does BSCF show the same feature? Would O₂^2-/O^- be helpful for SSCP as well?

Lines 151/152: The authors claim superior performance of SSCP over BSCF. However, the difference in performance as provided by j_max is only about 4%. What is the standard error for the results provided in this study? Please indicate reproducibility of the results.

Fig. 5: In the previous paper (doi.org/10.1016/j.electacta.2017.06.161, Ref. 29), BSCF showed j_OER = 172.7 mA/cm2. Here it is j_OER = 24 mA/cm2. Please check for consistency of the results. Did the authors confuse the corresponding surface area?

Line 186: Figure caption 5 reports 1 mV/s. Line 186 reports 0.1 mV/s for the same measurement.

Line 191: The authors refer to “someone else”. Please indicate who that would be.

Line 195-196: The authors argue that the effect of Co on the electrochemical activity of SSCP as compared to BSCF would be obvious. The reviewer would like to know what the standard error for the mass activity in the corresponding experiments would be. For this metric, the reported difference is about 1.5%, which is small to be significant. Moreover, according to the reviewers understanding, both investigated catalysts do contain Co. Please clarify.

Fig. 8: The authors report a potential of 1.590 V for SSCP at different current densities, but about 1.645 V for the stability test within the first hour. Please clarify and state reproducibility of the results.

Line 233/234: The authors refer to “numbers”. Which numbers are they referring to?

Fig. 9 does not provide any insight into the process of OER on SSCP. It is rather a table of content graphic. Consider deletion.

Line 247: The authors argue the investigated Zn-air battery would show discharge behavior at 1.2 V. The reviewer cannot see this in Fig. 10. Discharge appears to occur at 1.1V or slightly below. Consider enlargement and additional analysis for the data shown in Fig. 10.

Line 250: The authors argue it would be obvious that the Zn-air cell using SSCP as an OER catalyst had promising performance. Please provide literature reference to support this claim.

Fig. 10: The procedure of charge and discharge is unclear to the reviewer. Please clarify by proper description in the materials section as well as by proper indication of the applied current in Fig. 10.

Materials and methods section: According to the reviewer’s opinion, the degree of information provided in the materials and methods section is too low. Consider the addition of details (state: RDE equipment, RDE electrode area, number of reference runs, catalyst loading, full cell setup incl. drawing, oxygen supply, cycling procedure etc.).

Line 262: It is to the belief of the reviewer that H₂PtClO₄ does not exist. Please clarify.

Conclusion: According to the reviewer’s opinion at least the following statements in the conclusion are not sufficiently supported by the results provided in the manuscript:

• Structure and stoichiometry of SSCP -> not proven
• SSCP was a highly efficient OER electrocatalyst -> compare to commercial standard
• SSCP provides better Zn-air battery discharge performance -> no comparison provided
• Excellent SSCP performance due to high electronic conductivity -> data not shown nor discussed

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions for Authors

In their recent manuscript entitled: High-Performance A-site deficient Perovskite Electrocatalyst for Zn-Air Battery, Cheng Cheng Wang et al. report on the synthesis and the investigation of a novel catalyst material with respect to its electrocatalytic performance for the oxygen evolution reaction (OER). According to the author’s description, the synthesized material would be an A-site deficient perovskite containing, Sm, Sr, Co and Pt with the following stoichiometry: (SmSr)_0.95Co_0.9Pt_0.1O₃ (in the following abbreviated by: SSCP). For their investigation the authors applied XRD, SEM, HRTEM, HADDF, XPS, BET, LSV, CP and Zn-Air battery full cell testing. Based on their investigation, the authors claim SSCP would be a highly efficient OER electrocatalyst that exhibits high cycle stability.  

Research on the electrocatalytic properties of various perovskites for the OER is an extensively investigated branch of electrochemistry with a considerable number of papers published every year. However, despite this elevated number of papers, the manuscript provided by Cheng Cheng Wang et al. appears to be the first reporting on SSCP. Accordingly, the subject of the present manuscript is of general interest for the scientific community. Nevertheless, the reviewer cannot recommend the manuscript for publication in well-respected journal such as MDPI Catalysts (Impact Factor: 4.2), due to numerous unjustified statements, inconsistencies and an insufficient description of the results.   

These are the reviewer’s comments structured as follows: general comment, language and content.

General comment:

The reviewer recognizes the tendency to apply magniloquent terms in science in order to advertise own research. However, the reviewer does not agree that SSCP exhibits excellent electrocatalytic performance that justifies frequent repetition of this claim. This is due the following:

• SSCP is not compared to a commercial reference such as IrO₂nanoparticles, although it is the author’s intention to replace IrO₂ by a cheap alternative. Consider additional reference measurements for comparison.
• In his previous paper (org/10.1016/j.electacta.2017.06.161), Cheng Cheng Wang reports on a variety of different perovskites made of La, Sr, Ni and Fe (La₅Sr_0.5Ni_xFe_1-xO_3-δ, x=0.8, 0.5, 0.4, 0.2, LSNF55xx), which they compare to BSCF as well. In the previous study, LSNF 5546 was found to perform 14% better than the custom-made reference BSCF (based on j_OER). Nevertheless, in this manuscript, BSCF is chosen as a reference again, although in-house material showed better performance for a similar synthesis procedure already. Thus, in the reviewer’s opinion, SSCP cannot be considered an excellent material, since there are other materials (even without precious platinum reported by the same first author) which show even better performance. Thus, the reviewer recommends a less magniloquent description.

Language:

The quality of the English language throughout the complete manuscript is poor. The reviewer recommends professional language editing. Please pay special attention to missing definite and indefinite articles, tenses, missing and displaced words, as well as singular and plural inconsistencies. These are just a few examples from the first two manuscript pages:

Lines 15-16: Zinc-air batteries […]. However, THEIR application is. […]

Line 16: […] by slow kinetics of THE oxygen reduction [ORR] […]

Line 18: Here, AN A-site deficient […]

Line 74: Nanoparticles WERE similar to be […]

 Answer: We have already polished the language from the professional editing services.

Content:

Line 71: How would the others know the exact composition of the investigated material? The XRD pattern in Fig.1 does not provide a reference and the authors do not provide theoretic calculations of the expected XRD pattern. Moreover, the authors do not provide ICP-OES results in order to prove the validity of the proposed structure. Similarity with Sm_0.5Sr_0.5CoO₃ from reference [31] allows for other stoichiometries to result from the applied synthesis as well. Consider additional investigations.

Answer: Thanks for your suggestions. XPS technique was used in our study, so Pt element was definitely in the structure. We will try to use ICP technique to identify the exact amount of this perovskite in the next step.

Line 74: The authors claim an average nanoparticle size of 40-200 nm, which is a quite broad distribution. Moreover, the review is unable to determine how the authors determined the average nanoparticle size. Fig. 2a shows a large agglomerate with some distinct features. What are the actual particles? Moreover, the reviewer recommends to enlarge the scale bar.

Answer: Thanks for your suggestions. We have already enlarged the scale bar in the Fig2. Since we have enlarged the scale bar, it is easy for us to identify the average nanoparticle size distribution. Moreover, it will be easy for us to identify the roughly exact size by taking more SEM images.

Line 77: HADDF results are poorly explained despite their considerable consumption of space. 

Answer: Thanks for your suggestions. We have already analyzed the HADDF results in the manuscript.

Line 78: BET results are not shown in Fig.3

Answer: BET results were shown in Fig.6.

Line 129: The authors state that O₂^2-/O^- would be a reason for improved OER activity as stated by one of the indicated references (which reference is unclear to the reviewer). “Improved OER” is a relative term. Does BSCF show the same feature? Would O₂^2-/O^- be helpful for SSCP as well?

Answer: The reference was listed below. We also changed the description of improved OER activity.

[1] Liu, R.; Liang, F.; Zhou, W.; Yang, Y. and Zhu, Z., Calcium-doped lanthanum nickelate layered perovskite and nickel oxide nano-hybrid for highly efficient water oxidation. Nano Energy, 2015. 12: 115-122.

[2] Jung, J.-I.; Jeong, H.Y.; Lee, J.-S.; Kim, M.G. and Cho, J., A Bifunctional Perovskite Catalyst for Oxygen Reduction and Evolution. Angewandte Chemie International Edition, 2014. 53(18):4582-4586.

BSCF was also showing the feature, according to what we have been searched for some published papers. The title of the paper was “A hexagonal perovskite Ba_0.9Sr_0.1Co_0.8Fe_0.1Ir_0.1O_3-# as an efficient electrocatalyst towards oxygen evolution reaction”. In this paper, the XPS of O spectra also clearly identified the O₂^2-/O^- would be beneficial for improved OER activity.

Lines 151/152: The authors claim superior performance of SSCP over BSCF. However, the difference in performance as provided by j_max is only about 4%. What is the standard error for the results provided in this study? Please indicate reproducibility of the results.

Answer: We have already rechecked the data and listed the updated the figure in the manuscript.

Fig. 5: In the previous paper (doi.org/10.1016/j.electacta.2017.06.161, Ref. 29), BSCF showed j_OER = 172.7 mA/cm2. Here it is j_OER = 24 mA/cm2. Please check for consistency of the results. Did the authors confuse the corresponding surface area?

Answer: In our previous published paper, BSCF showed j_OER = 172.7 mA/cm², it is mainly because that the electrocatalyst was tested in 1 M KOH, however, in this paper, BSCF was tested in 0.1 M KOH. The difference in the concentration of electrolyte KOH can lead to the difference of current density tested.

Line 186: Figure caption 5 reports 1 mV/s. Line 186 reports 0.1 mV/s for the same measurement.

Answer: We have already changed the scan rate of 1 mV/s.

Line 191: The authors refer to “someone else”. Please indicate who that would be.

Answer: We have already added the name of the author.

Line 195-196: The authors argue that the effect of Co on the electrochemical activity of SSCP as compared to BSCF would be obvious. The reviewer would like to know what the standard error for the mass activity in the corresponding experiments would be. For this metric, the reported difference is about 1.5%, which is small to be significant. Moreover, according to the reviewers understanding, both investigated catalysts do contain Co. Please clarify.

Answer: Sorry for our wrong explanation. According to the structure of this perovskite SSCP, one of the main difference is due to the Pt element existing in the structure instead of Co, comparing with BSCF. 

Fig. 8: The authors report a potential of 1.590 V for SSCP at different current densities, but about 1.645 V for the stability test within the first hour. Please clarify and state reproducibility of the results.

Answer: Thanks for your suggestions to reproduce the results. We have already identified the results of the stability and put them in the manuscript.

Line 233/234: The authors refer to “numbers”. Which numbers are they referring to?

Answer: We have already added the numbers that are referring to the current density.

Fig. 9 does not provide any insight into the process of OER on SSCP. It is rather a table of content graphic. Consider deletion.

Answer: We have already deleted this figure.

Line 247: The authors argue the investigated Zn-air battery would show discharge behavior at 1.2 V. The reviewer cannot see this in Fig. 10. Discharge appears to occur at 1.1 V or slightly below. Consider enlargement and additional analysis for the data shown in Fig. 10.

Answer: Thanks for your suggestions. We have rechecked the data and changed them in the manuscript.

Line 250: The authors argue it would be obvious that the Zn-air cell using SSCP as an OER catalyst had promising performance. Please provide literature reference to support this claim.

Fig. 10: The procedure of charge and discharge is unclear to the reviewer. Please clarify by proper description in the materials section as well as by proper indication of the applied current in Fig. 10.

Answer: The detailed procedure of testing Zn-air battery can be found in some literatures. One of the papers was listed below.

[1] Wu, X. Y.; Miao, H.; Hu, R. G.; Chen, B.; Yin, M. M.; Zhang, H. C.; Xia, L.; Zhang, C. F.; Yuan, J. L., A-Site Deficient Perovskite Nanofibers Boost Oxygen Evolution Reaction for Zinc-Air Batteries, Applied Surface Science, 2021, 536.

Materials and methods section: According to the reviewer’s opinion, the degree of information provided in the materials and methods section is too low. Consider the addition of details (state: RDE equipment, RDE electrode area, number of reference runs, catalyst loading, full cell setup incl. drawing, oxygen supply, cycling procedure etc.).

Answer: We have already added more detailed information in the materials and methods section.

Line 262: It is to the belief of the reviewer that H₂PtClO₄ does not exist. Please clarify.

Answer: H₂PtClO₄ was used as raw materials in the experimental part and EDS elemental mapping of Pt was also shown in the discussion part.

Conclusion: According to the reviewer’s opinion at least the following statements in the conclusion are not sufficiently supported by the results provided in the manuscript:

• Structure and stoichiometry of SSCP -> not proven
• SSCP was a highly efficient OER electrocatalyst -> compare to commercial standard
• SSCP provides better Zn-air battery discharge performance -> no comparison provided
• Excellent SSCP performance due to high electronic conductivity -> data not shown nor discussed

Answer: Thanks for the reviewer’s comments. We have already rewritten the conclusion in order to make the description more reasonable.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Considering this second version of the article I can say that there have been some improvements, but the authors have not taken into account my observation about the comments of the Tafel slope.
A change in the Tafel slope in electrocatalytic processes, involving adsorption processes such as RDS, could be due to many factors, which they do not consider, attributing this behavior to an increase in electron transfer. A discussion on these different causes should be included.

Reviewer 2 Report

The reviewer considered the revised version of “High-Performance A-site deficient Perovskite Electrocatalyst for Zn-Air Battery” by C. Wang et al. for publication in MDPI Catalysts. The reviewer acknowledges the intention of the authors to improve their manuscript. Some progress has been made. However, the quality of the manuscript is still not high enough to justify a dissemination in MDPI Catalysts. In fact, several comments of the reviewer have not been addressed or were not met appropriately. Moreover, some changes appear arbitrary to the reviewer. Therefore, the reviewer still opts to reject the manuscript.

These are some comments as a reply to the answers of the authors to the initial review:

The quality of the English language throughout the complete manuscript is poor. The reviewer recommends professional language editing. Please pay special attention to missing definite and indefinite articles, tenses, missing and displaced words, as well as singular and plural inconsistencies. These are just a few examples from the first two manuscript pages:

Lines 15-16: Zinc-air batteries […]. However, THEIR application is. […]

Line 16: […] by slow kinetics of THE oxygen reduction [ORR] […]

Line 18: Here, AN A-site deficient […]

Line 74: Nanoparticles WERE similar to be […]

Answer: We have already polished the language from the professional editing services.

Reviewer reply: Language quality still poor. Tenses and use of articles to be improved.

Line 71: How would the others know the exact composition of the investigated material? The XRD pattern in Fig.1 does not provide a reference and the authors do not provide theoretic calculations of the expected XRD pattern. Moreover, the authors do not provide ICP-OES results in order to prove the validity of the proposed structure. Similarity with Sm_0.5Sr_0.5CoO₃ from reference [31] allows for other stoichiometries to result from the applied synthesis as well. Consider additional investigations.

Answer: Thanks for your suggestions. XPS technique was used in our study, so Pt element was definitely in the structure. We will try to use ICP technique to identify the exact amount of this perovskite in the next step.

Reviewer reply: Authors still neither provide evidence for the validity of the proposed structure nor the actual stoichiometry.

Line 74: The authors claim an average nanoparticle size of 40-200 nm, which is a quite broad distribution. Moreover, the review is unable to determine how the authors determined the average nanoparticle size. Fig. 2a shows a large agglomerate with some distinct features. What are the actual particles? Moreover, the reviewer recommends to enlarge the scale bar.

Answer: Thanks for your suggestions. We have already enlarged the scale bar in the Fig2. Since we have enlarged the scale bar, it is easy for us to identify the average nanoparticle size distribution. Moreover, it will be easy for us to identify the roughly exact size by taking more SEM images.

Reviewer reply: The reviewer is still unable to differentiate individual particles. Fig. 2a shows one large agglomerate in the µm size range. If other SEM images show individual particles, consider replacement.

Lines 151/152: The authors claim superior performance of SSCP over BSCF. However, the difference in performance as provided by j_max is only about 4%. What is the standard error for the results provided in this study? Please indicate reproducibility of the results.

Answer: We have already rechecked the data and listed the updated the figure in the manuscript.

Reviewer reply: SSCP has a positive offset now, while BSCF has a negative offset. The reviewer would like to know the reason.

Line 195-196: The authors argue that the effect of Co on the electrochemical activity of SSCP as compared to BSCF would be obvious. The reviewer would like to know what the standard error for the mass activity in the corresponding experiments would be. For this metric, the reported difference is about 1.5%, which is small to be significant. Moreover, according to the reviewers understanding, both investigated catalysts do contain Co. Please clarify.

Answer: Sorry for our wrong explanation. According to the structure of this perovskite SSCP, one of the main difference is due to the Pt element existing in the structure instead of Co, comparing with BSCF.

Reviewer reply: The authors corrected for Pt instead of Co. Nevertheless, the core of the question remains. The authors argue that the effect of Pt on the electrochemical activity of SSCP as compared to BSCF would be obvious. The reviewer would like to know what the standard error for the mass activity in the corresponding experiments would be. For this metric, the reported difference is about 1.5%, which is small to be significant.

Line 233/234: The authors refer to “numbers”. Which numbers are they referring to?

Answer: We have already added the numbers that are referring to the current density.

Reviewer reply: The reviewer acknowledges the changes to the figure caption. However, a second y-axis would be even better to indicate the meaning of the “numbers”.

Line 250: The authors argue it would be obvious that the Zn-air cell using SSCP as an OER catalyst had promising performance. Please provide literature reference to support this claim.

Reviewer comment: No comparison provided.

Fig. 10: The procedure of charge and discharge is unclear to the reviewer. Please clarify by proper description in the materials section as well as by proper indication of the applied current in Fig. 10.

Answer: The detailed procedure of testing Zn-air battery can be found in some literatures. One of the papers was listed below.

[1] Wu, X. Y.; Miao, H.; Hu, R. G.; Chen, B.; Yin, M. M.; Zhang, H. C.; Xia, L.; Zhang, C. F.; Yuan, J. L., A-Site Deficient Perovskite Nanofibers Boost Oxygen Evolution Reaction for Zinc-Air Batteries, Applied Surface Science, 2021, 536.

Materials and methods section: According to the reviewer’s opinion, the degree of information provided in the materials and methods section is too low. Consider the addition of details (state: RDE equipment, RDE electrode area, number of reference runs, catalyst loading, full cell setup incl. drawing, oxygen supply, cycling procedure etc.).

Answer: We have already added more detailed information in the materials and methods section.

Reviewer reply: The reviewer would like to remind the authors that the purpose of the Experimental Section is to elucidate all procedures that were applied to achieve the presented data. Neither Fig. 9, nor the Experimental Section nor a reference provide the procedure in the manuscript. Moreover, the reviewer asks this question since the cell voltage profile appears to differ from simple repetitive charge/discharge. Please clarify.

Line 262: It is to the belief of the reviewer that H₂PtClO₄ does not exist. Please clarify.

Answer: H₂PtClO₄ was used as raw materials in the experimental part and EDS elemental mapping of Pt was also shown in the discussion part.

Reviewer reply: The reviewer asks the authors to provide the CAS-number of H₂PtClO_4.